Conventional magnetic storage devices generally include a magnetic transducer head suspended in close proximity to a recording medium, such as a magnetic disk having a plurality of concentric tracks. The storage device also includes a spindle motor for rotating the disk and a head stack assembly that can include one or more read/write heads. The head stack assembly is controllably positioned over the magnetic disk by an actuator or a servo system in order to read or write information from or to particular tracks on the disk.
When the disk is at rest, the heads normally ride just resting on the disk; however, when the disk is spinning, air forces generated between the disk and the heads cause the heads to float a small distance above the magnetic media.
Two of the most critical periods in determining the read/write head life span occur during take off and landing. Prior to operation, the read/write head rests on an inner track or landing zone where the head is parked. As the disk begins to rotate from an initial, stopped position, the read/write head is dragged along the surface of the disk. Once the disk reaches sufficient speed, the aerodynamic lift floats the read/write head assembly away from the disk surface.
During shutdown of the disk drive system, the disk drive spindle motor slows and the air forces begin to stop, allowing the heads to fall into contact with the magnetic media. If the heads come into contact with the media while there is still some movement of the media, wear or damage may result, both to the recorded area on the media and to the heads.
Consequently, means have been proposed to position the heads over a “landing strip” portion of the disk, so that only that strip is damaged by a head falling onto the disk. This landing strip is typically along the inner diameter (ID) of the magnetic disk surface. In the event of a loss of power, to prevent the heads from landing on portions of the magnetic media other than the ID, often when a power failure is detected, the motor spinning the disk is allowed to continue to turn under the inertia of the various masses of the drive. As a result, the spindle motor coils generate their own back-emf. The coils of the spinning motor are then connected to deliver the voltages generated by the back-emf produced in the motor windings to operate retract control circuitry and to provide the energy to the voice coils necessary to drive the heads to the landing strip. Once the head is retracted to the ID and the air forces stop, the head falls and contacts the disk surface, the head is dragged across the ID surface as the motor's momentum continues the magnetic disk rotation for a period before a brake is finally applied to totally stop the motor. Power failure detection, back-emf utilization, head retract circuitry, and motor braking are known in the art.